P-selectin and PSGL-l are cell adhesion molecules that play a critical role in the inflammatory response in the vasculature. This laboratory discovered P-selectin on the surface of activated platelets and established its role as an adhesion molecule in mediating platelet and endothelial cell binding to leukocytes. In collaboration with Genetics Institute, this laboratory also identified and expression cloned the P-selectin counter receptor, PSGL-1, an adhesion molecule resident on myeloid cells and certain T lymphocytes. Over the past several years, this laboratory has developed a PSGL-1 nul mouse using standard gene disruption techniques. These animals are viable but have not been characterized to date. The proposed Pilot & Feasibility Project will explore the use of this mouse model within the context of its role in cutaneous inflammation. This work will be greatly facilitated by the available core resources in the Harvard Skin Diseases Research Center. The homozygous PSGL-1 nul mouse, PSGL-1 (-/-), and the heterozygous PSGL-1 mouse (+/-) allow for the development of a new animal model to explore the physiologic importance of PSGL-1 in vivo, with special reference to the role of PSGL-1 in the inflammatory response in skin. The PSGL-1 (-/-) mouse colony and the PSGL-1 (+/-) mouse colony will be expanded and these animals characterized in detail. This will include determination of the phenotype of these animals over the lifetime of the animal: white blood cell count, susceptibility to infection, presence or absence of skin lesions, organ histology. The physiologic role of PSGL-l will be examined vis a vis E-selectin and P-selectin function. Using a parallel plate rolling assay, the ability of PSGL-l (-/-) neutrophils and T lymphocytes to roll on a surface defined by E-selectin and P-selectin will be determined. By flow cytometry, T lymphocytes from PSGL-1 (-/-), (+/-) and (+/+) mice will be examined for the expression of cutaneous lymphocyte antigen (CLA) to determine whether CLA is a component of PSGL-l. Finally, new animal models of inflammation and leukocyte recruitment will be examined in this mouse model in vivo. The studies represent Pilot and Feasibility Studies of the application of the PSGL-1 nul mouse model to the examination of the role of PSGL-1 in cutaneous pathology.